The present invention relates to cooling passages in hot component parts. More particularly, the present invention relates to improved cooling passages and methods of fabrication in, for example, turbine engine components.
In many current systems having cooled parts, for example gas turbine engines, the cooled hot gas path components typically use a variety of internal passages through which the cooling fluid is passed to maintain the bulk temperature of the part at some acceptable temperature level.
In many locations, these passages are of circular cross-section. For such circular passages, there are two main types of surfaces used for heat transfer, smooth surfaces and turbulated surfaces using transverse rib rougheners. An additional possible heat transfer enhancement surface is the use of a helical rib element within the circular passage, but this type of feature is not amenable to conventional investment casting, electro-discharge machining or electro-chemical machining methods.
There is a need in the art for improved cooling passages that provide improved heat transfer characteristics or improved pressure drop characteristics and there is an additional need for improved methods of fabricating these cooling passages.
A turbine portion, for example a turbine blade, for exposure in a hot fluid flow includes at least one internal cooling passage disposed therein. A cooling fluid is introduced within the cooling passage(s) to maintain the bulk temperature of the turbine portion at some acceptable temperature level. A plurality of concavities are disposed on the interior surface of the cooling passage. In one embodiment, the concavities are formed on the interior surface of cooling passage in an array pattern such that a spiral bulk fluid motion is obtained, similar to that which would be formed by a helical rib, but without the rib. The concavity surface pattern serves to enhance heat transfer to the same degree as conventional rib rougheners, but with significantly less pressure loss due to friction. The spiral motion of the bulk cooling fluid also serves to recirculate central coolant to the heat transfer surface, thereby making the heat exchange process more effective than that for turbulated surfaces.